This invention relates to a drying carrier adapted for carrying honeycomb structures.
Such a drying carrier may be used when the honeycomb structures are dried through a drying apparatus as shown in FIG. 1 which illustrates a dielectric and ventilation type drying apparatus including a dielectric drying zone 101 and a ventilation drying zone 102. In drying the honeycomb structure, the honeycomb structures 3 are carried on a carrier 1 in such a manner that the open bottom surface of the honeycomb structure 3 contacts the upper surface of the carrier 1. The honeycomb structure 3 is a ceramic green structure which is extrusion molded from a batch of a ceramic material through an extrusion die and has number of parallel through holes separated by partitions having a uniform thickness.
The honeycomb structures 3 carried on the carrier 1 are continuously moved through the dielectric drying zone 101 and the ventilation drying zone 102 by means of a dielectric drying conveyor 111 and a ventilation drying conveyor 112 and dried in this moving step.
The dielectric drying zone 101 includes upper and lower electrodes 113 which are arranged in parallel to the open end surfaces of the honeycomb structure and hot air ventilating ducts 114 for blowing hot air into the drying zone to prevent steam generated during drying from condemning on the surfaces of the electrodes 113 or the drying zone 101.
The honeycomb structures 3 are then transferred to the ventilation drying zone 102 by means of a ventilation drying conveyor 112 in order to completely dry the honeycomb structures after dielectric drying. In the ventilation drying zone 102, hot air of 80.degree..about.150.degree. C. is blown at a speed 0.3.about.2.0 m/sec into the ventilation drying zone by means of hot air ventilating ducts 115 to dry the honeycomb structures 3 by ventilating.
Thus, the honeycomb structures 3 are subjected to a sequence of dielectric drying and ventilation drying through the dielectric and ventilation drying apparatus by using the carrier. In FIG. 1, a steam discharge duct is denoted by a numeral 116.
A drying carrier adapted for carrying honeycomb structures in the drying apparatus including the dielectric drying zone as mentioned above has been proposed by applicants (ref. Japanese Patent application Publication No. 60-37382). This drying carrier includes perforated plates having an area including a portion contacting with an open bottom surface of the honeycomb structure and a conductivity higher than that of the remaining portion of the drying carrier as shown in FIGS. 2 and 3. That is, the drying carrier 1 has a hole 2 having a dimension larger than the bottom surface of the honeycomb structure 3 to be carried and a perforated plate 4 made of a material having a conductivity higher than that of the carrier 1 is securely fitted in the hole 2. When the honeycomb structures are dried by use, of such a drying carrier, particularly during dielectric drying, the occurrence of cracks in the honeycomb structure is prevented in the subsequent sintering step. Thus, the proposed drying carrier is superior to the conventional drying carrier so that the quality and productivity of various honeycomb structures such as cordierite, mullite, silicon nitride and the like are improved.
However perforated plate 4 of the proposed drying carrier is flat and has an upper contacting surface area larger than that of the bottom surface of the honeycomb structure to be dried. Therefore, when the honeycomb structure shrinks during drying, the shrinkage of the bottom portion of the honeycomb structure is prevented because of a fractional resistance between the surfaces of the bottom of the honeycomb structure and the perforated plate. Consequently, the honeycomb structure is deformed to deteriorate the dimensional accuracy thereof so that the yield becomes low when a high dimensional accuracy is required. Furthermore, the fractional resistance causes a shrinkage strain to generate in the bottom surface of the honeycomb structure thus resulting in cracks in the bottom surface. Thus, the frictional resistance adversely affects the quality of the products.